Up to 8000 families, couples and individuals trying to get into their first home will be stymied by the Reserve Bank's new lending restrictions, Finance Minister Bill English has acknowledged.

But Labour finance spokesman David Parker says the tally is probably even higher than that and Aucklanders will be hardest hit.

Mortgage brokers are working around the clock trying to process as many pre-approved loans as possible to reduce the number of people who will miss out.

The political argument over the Reserve Bank's new limits on lending to home buyers with deposits of less than 20 per cent continued yesterday as Mr Parker asked Mr English how many first-home buyers in Auckland would be excluded from the market.

Mr English said no estimates had been given on the numbers excluded from Auckland or any other market.

But the Reserve Bank had advised him that of the 20,000 to 30,000 first-home buyers each year, 13,000 to 19,000 obtained a high loan-to-value ratio (LVR) loan.

Under the Reserve Bank's new rules, which allow commercial banks to make only 10 per cent of their new residential mortgage lending to buyers borrowing more than 80 per cent of the value of the property, 12,000 of those would still get a loan, Mr English told Parliament.

"The remaining 6000 to 8000 will make the choice of looking at a cheaper property or delaying their purchase while they save a higher deposit."

Mr English said the numbers were difficult to estimate, and didn't take into account the Government's policies in support of first-home buyers.

"What shuts them out of the market in the long run is a shortage of houses to buy, which is their bigger problem right now, or high interest rates," he told the Herald later.

Mr Parker said the figures revealed the loan limits would have "a significant effect on first-home buyers".

He also said the Reserve Bank's estimate of up to 8000 first-home buyers being affected was not necessarily accurate.

"I suspect the number's higher than that. This is going to bite hardest in Auckland where a third of New Zealand lives and where it's hardest to get a deposit of more than 20 per cent because house prices are so high."

The industry was predicting nearly a fifth of low-deposit borrowers would be locked out.

"Whatever the number is, it's basically 15 to 20 per cent of the market that will be removed, so whatever way you look at it that's a significant chunk of people that could be buying a property that won't be able to."

The policy, in effect from October 1, has already hit some first-home buyers - ASB Bank this week cancelled pre-approvals for low-equity home loans from October 4.

Credit bureau Veda's managing director John Roberts said the company had seen a surge in mortgage inquiries from younger and most likely first-home buyers since the loan limits were announced.